Discrimination and Analysis of Several Concepts about 485 Bus of Access Control System

Concept 1: The communication distance of 485 bus can reach 1200 meters.

In fact, it is just the theory of 485 bus structure

Under the premise of an ideal environment, it is possible to make the transmission distance reach 1200 meters. Generally speaking, it means that the communication wire is of high quality and meets the standard. The baud rate is 9600. Only one 485 device can make the communication distance reach 1200 meters, and the ability to communicate does not mean that every communication is normal. Therefore, the actual stable communication distance of the 485 bus is usually far less than 1200 meters.

There are many load 485 devices, the wire impedance is not up to standard, the wire diameter is too thin, the converter quality is poor, the device lightning protection, the baud rate is increased and other factors will reduce the communication distance.

Concept 2: The 485 bus can carry 128 devices for communication.

In fact, not all 485 converters can carry 128 access controller devices. It should be judged according to the model adopted by the chip in the 485 converter and the model adopted by the 485 device chip. Whoever is lower There are generally three levels of 485 chip load capacity

32 sets 128 sets 256 sets.

Theoretical nominals are often not actually achieved. The longer the communication distance, the higher the baud rate, the thinner the wire diameter, the worse the wire quality, the worse the converter quality, the insufficient power supply of the converter (passive converter), the stronger the lightning protection, these will greatly reduce the real load Quantity.

Concept 3: The 485 bus is a simplest, most stable and mature industrial bus structure.

This concept is wrong. It should be: 485 bus is an economical traditional industrial bus used for device networking. Communication quality needs to be tested and debugged according to construction experience.

Although the 485 bus is simple, it must be strictly installed and constructed for wiring.